1. Field of Invention
The teachings presented herein relate to electronic circuitry. More specifically, the teachings relate to methods and systems for digital data coding and electronic circuits incorporating the same.
2. Discussion of Related Art
A/D and D/A converters are widely used in the industry of electronics. In converting an analog signal to a digital signal, the analog signal is sampled at discrete points according to a certain frequency. Voltages of the analog signal at such sampled points are measured. Each measured voltage at a sampling point is then coded using a digital code having a plurality of binary bits. Such a digital code can be used to represent the sampled analog value and can be transmitted in a digital means to a destination. Once the digital code representing an analog value is received by a receiver, the digital code can be decoded by a D/A converter to derive an estimated voltage that is similar to the original voltage being coded. FIG. 1(a) shows a typical A/D and D/A processing flow. In FIG. 1(a), an A/D converter 110 takes an analog signal A as input and generates a digital code B as an output. The digital code B is often processed by a digital signal processor 115 to generate a digital signal C. When digital signal C is transmitted and received by a receiver 120, which may then apply a D/A process at a D/A converter 130 and produces a recovered analog signal C′ based on digital signal C.
A digital code representing a particular sampled voltage of the analog signal is conventionally determined, by the A/D converter 110 based on a look-up table in accordance with the voltage level of the sample. For example, FIG. 1(b)(Prior Art) depicts a typical A/D converter 110. An analog signal A is sampled first by an analog sampling unit 140 to produce individual analog voltages as an output. For each such analog voltage, an A/D look-up unit 150 determines a digital code representing the analog voltage based on a look-up table 160.
A D/A converter reverses the process to convert a digital code to generate an analog voltage represented by the digital code. This is shown in FIG. 1(c) (Prior Art), where a D/A look-up unit 170 in a D/A converter 130 consults with the look-up table 160 based on a received digital code C to produce an analog voltage. The represented analog voltage is then sent to an analog signal generator 180, which may utilize different analog voltages to produce an estimated analog signal C′.
FIG. 1(d) (Prior Art) shows an exemplary look-up table 160 in which the left column 190 lists various ranges of analog voltages and, correspondingly, the right column 195 provides 14-bit digital codes for different voltage ranges. For instance, for a zero voltage, the digital code is “00 0000 0000 0000”. For a voltage between +0.000122 v and +0.000244 v, the corresponding digital code is “00 0000 0000 0001”. For a voltage between −0.000122 v and −0.000244, the corresponding digital code is “11 1111 1111 1111”, etc.
In accordance with the conventional look-up table, as shown in FIG. 1(d) (Prior Art), when an analog signal crosses 0V in a negative direction, all the binary bits of the digital code change state from 0 to 1. When a large number of digital outputs change at the same time in the same direction (from 1's to 0's or from 0's to 1s), noise current on the circuit board is induced because the output load capacitances are charged and discharged. In various applications such as communications, it is common to have an analog signal centered at 0 v and such an analog signal may also have frequent deviations from 0V. Consequently, all binary bits of a digital code will frequently change states which make the problem worse.
A previous solution for reducing digital noise is Gray Coding, as disclosed in U.S. Pat. No. 2,632,058 issued to F. Gray. This method solves the problem by allowing only one bit changing state between any two adjacent codes. Although such a solution solves the problem, a disadvantage of this approach is that its implementation requires complex circuitry for coding and decoding data. Therefore, a solution that both reduces digital noise and is cost effective is needed.